Two loudspeakers placed on opposite sides of a small auditorium are driven by separate signal generators. One generator is set to 440 Hz (the concert-pitch A), while the other is set to 444 Hz. An audience member standing midway between the speakers notices that the sound alternates between loud and soft even though each speaker emits a continuous tone of constant amplitude.
(a) Identify the acoustic phenomenon responsible for the periodic variations in loudness heard by the audience member.
(b) Explain, in terms of the principle of superposition, how two steady sound waves of slightly different frequency can produce a single sound whose amplitude varies with time.
(c) The listener reports that the loud–soft cycle repeats several times each second but that only one pitch is perceived rather than two distinct notes. Using the information given and typical characteristics of human hearing, describe why the listener hears a single tone that seems to fluctuate in volume instead of two separate pitches.